Method and surface morphology of non-polar gallium nitride containing substrates

ABSTRACT

An optical device, e.g., LED, laser. The device includes a non-polar gallium nitride substrate member having a slightly off-axis non-polar oriented crystalline surface plane. In a specific embodiment, the slightly off-axis non-polar oriented crystalline surface plane is up to about −0.6 degrees in a c-plane direction, but can be others. In a specific embodiment, the present invention provides a gallium nitride containing epitaxial layer formed overlying the slightly off-axis non-polar oriented crystalline surface plane. In a specific embodiment, the device includes a surface region overlying the gallium nitride epitaxial layer that is substantially free of hillocks.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/182,107 filed May 29, 2009, entitled “METHOD AND SURFACEMORPHOLOGY OF NON-POLAR GALLIUM NITRIDE CONTAINING SUBSTRATES” byinventors JAMES W. RARING and CHRISTIANE POBLENZ, commonly assigned andincorporated by reference herein for all purposes

BACKGROUND OF THE INVENTION

The present invention is directed to optical devices and relatedmethods. More particularly, the present invention provides a method anddevice for fabricating crystalline films for emitting electromagneticradiation using non-polar gallium containing substrates such as GaN, MN,InN, InGaN, AlGaN, and AlInGaN, and others. Merely by way of example,the invention can be applied to optical devices, lasers, light emittingdiodes, solar cells, photoelectrochemical water splitting and hydrogengeneration, photodetectors, integrated circuits, and transistors, amongother devices.

In the late 1800's, Thomas Edison invented the conventional light bulb.The conventional light bulb, commonly called the “Edison bulb,” has beenused for over one hundred years for a variety of applications includinglighting and displays. The conventional light bulb uses a tungstenfilament enclosed in a glass bulb sealed in a base, which is screwedinto a socket. The socket is coupled to an AC power or DC power source.The conventional light bulb can be found commonly in houses, buildings,and outdoor lightings, and other areas requiring light or displays.Unfortunately, drawbacks exist with the conventional Edison light bulb.

First, the conventional light bulb dissipates much thermal energy. Morethan 90% of the energy used for the conventional light bulb dissipatesas thermal energy.

Secondly, reliability is an issue since the conventional light bulbroutinely fails often due to thermal expansion and contraction of thefilament element.

Thirdly, light bulbs emit light over a broad spectrum, much of whichdoes not result in bright illumination due to the spectral sensitivityof the human eye.

Lastly, light bulbs emit in all directions and are not ideal forapplications requiring strong directionality or focus such as projectiondisplays, optical data storage, or specialized directed lighting.

In 1960, Theodore H. Maiman demonstrated the first laser at HughesResearch Laboratories in Malibu. This laser utilized a solid-stateflashlamp-pumped synthetic ruby crystal to produce red laser light at694 nm. By 1964, blue and green laser output was demonstrated by WilliamBridges at Hughes Aircraft utilizing a gas laser design called an Argonion laser. The Ar-ion laser utilized a noble gas as the active mediumand produce laser light output in the UV, blue, and green wavelengthsincluding 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm,496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laser had thebenefit of producing highly directional and focusable light with anarrow spectral output, but the wall plug efficiency was <0.1%, and thesize, weight, and cost of the lasers were undesirable as well.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green lasers. As aresult, lamp pumped solid state lasers were developed in the infrared,and the output wavelength was converted to the visible using specialtycrystals with nonlinear optical properties. A green lamp pumped solidstate laser had 3 stages: electricity powers lamp, lamp excites gaincrystal which lases at 1064 nm, 1064 nm goes into frequency conversioncrystal which converts to visible 532 nm. The resulting green and bluelasers were called “lamped pumped solid state lasers with secondharmonic generation” (LPSS with SHG) had wall plug efficiency of ˜1%,and were more efficient than Ar-ion gas lasers, but were still tooinefficient, large, expensive, fragile for broad deployment outside ofspecialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nmgoes into frequency conversion crystal which converts to visible 532 nm.The DPSS laser technology extended the life and improved the wall plugefficiency of the LPSS lasers to 5-10%, and further commercializationensue into more high end specialty industrial, medical, and scientificapplications. However, the change to diode pumping increased the systemcost and required precise temperature controls, leaving the laser withsubstantial size, power consumption while not addressing the energystorage properties which made the lasers difficult to modulate at highspeeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulateable, theysuffer from severe sensitivity to temperature which limits theirapplication. These and other limitations may be described throughout thepresent specification and more particularly below.

From the above, it is seen that techniques for improving optical devicesis highly desired.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, techniques related generally tooptical devices are provided. More particularly, the present inventionprovides a method and device for fabricating crystalline films foremitting electromagnetic radiation using non-polar gallium containingsubstrates such as GaN, MN, InN, InGaN, AlGaN, and AlInGaN, and others.Merely by way of example, the invention can be applied to opticaldevices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors, among otherdevices. In a preferred embodiment, the optical device is a laser thathas been configured for blue and green emissions, as well as others. Instill a preferred embodiment, the optical device is an LED that has beenconfigured for blue emission, as well as others.

In a specific embodiment, the present invention provides a method andresulting nonpolar m-plane (10-10) oriented gallium nitride structure(e.g., gallium and nitrogen containing structure, gallium nitridestructure) having smooth surface morphology, which is oftensubstantially free from hillocks and the like. In one or moreembodiments, the method includes using a miscut or offcut surface or nomiscut or offcut or other off-axis orientation of a non-polar m-planesurface orientation as a growth surface region. In a preferredembodiment, the epitaxial layer is configured using at least anatmospheric pressure (e.g. 700-800 Torr) epitaxial formation process,but may also be configured for other processes. In a specificembodiment, the method includes use of a N₂ carrier and subflow gas,which is substantially all N₂, as a medium for precursor gases, whichform the crystalline gallium nitride epitaxial material (e.g., galliumand nitrogen containing epitaxial material). The growth using thesubstantially predominant N₂ gas leads to formation of crystallinegallium nitride epitaxial material substantially free of hillocks andthe like. Of course, there can be other variations, modifications, andalternatives. As used herein, the term “nonpolar (10-10) orientedgallium nitride structure” refers to the family of nonpolar m-plane(10-10) oriented gallium nitride structures, nonpolar m-plane (10-10)oriented gallium and nitrogen containing structures, and the like.

In an alternative preferred embodiment, the present invention includesuse of a gallium nitride substrate configured in a non-polar (10-10)surface orientation that has a miscut towards the c-plane (0001) rangingfrom about −0.6 degrees to about −2.0 degrees and any miscut towards thea-plane (11-20) although there can be other orientations and degrees ofmiscut or offcut or off-axis orientation. In one or more embodiments,the method uses an H₂ carrier gas and combination of H₂ and N₂ subflowgases in further combination with precursor gases for growth ofcrystalline gallium nitride epitaxial material. In still a preferredembodiment, the miscut can be about −0.8 degrees to about −1.1 degreestoward the c-plane (0001) and between −0.3 degrees and 0.3 degreestowards the a-plane (11-20) to cause formation of an overlying galliumnitride epitaxial layer with smooth morphology. Of course, there can beother variations, modifications, and alternatives.

Still further, the present invention provides an optical device that hasepitaxial film that is substantially free from morphological features onthe surface such as hillocks and the like. In a specific embodiment thedevice has a non-polar (10-10) gallium nitride substrate member having aslightly off-axis non-polar oriented crystalline surface plane. In oneor more embodiments, the slightly off-axis (or on-axis) non-polaroriented crystalline surface plane ranges from about 0 degrees to apredetermined degree toward either or both the c-plane and/or a-plane.In a specific embodiment, the device has a gallium nitride containingepitaxial layer formed overlying the slightly off-axis non-polaroriented crystalline surface plane. A surface region is overlying thegallium nitride epitaxial layer. In a preferred embodiment, the surfaceregion being substantially free from hillocks having an average spatialdimension of, for example, 10-100 microns and greater, but can be otherdimensions. In a preferred embodiment, the epitaxial layer is configuredusing at least an atmospheric pressure (e.g. 700-800 Torr) epitaxialformation process. In a specific embodiment, the epitaxial layercomprises one or more layers which form at least a quantum well of atleast 3.5 nanometers and greater or other desirable dimensions. Thequantum well, which is thicker, leads to improved laser devices.

Still further, the present invention provides a method of fabricating anoptical device. The method includes providing a non-polar (10-10)gallium nitride substrate member having a slightly off-axis non-polaroriented crystalline surface plane. In a specific embodiment, theslightly off-axis non-polar oriented crystalline surface plane isgreater in magnitude than about negative 0.6 degrees toward the c-plane(0001) or other desirable magnitudes. The method includes forming agallium nitride containing epitaxial layer having a smooth surfaceregion substantially free of hillocks overlying the slightly off-axisnon-polar oriented crystalline surface plane.

In yet other embodiments, the present invention provides a method offabricating an alternative optical device. The method includes providinga non-polar (10-10) gallium nitride substrate member having a slightlyoff-axis non-polar oriented crystalline surface plane in a specificembodiment. The slightly off-axis non-polar oriented crystalline surfaceplane ranges from about 0 degrees to a predetermined degree towardeither or both the c-plane or a-plane. In a specific embodiment, thepresent method includes forming a gallium nitride containing epitaxiallayer, using at least an atmospheric pressure (e.g. 700-800 Torr)epitaxial process to form at least a quantum well having a thickness ofat least 3.5 nanometers and greater or other desirable dimensions.Preferably, the gallium nitride epitaxial layer has a surface regionsubstantially smooth and free from hillocks.

As used herein, the term “miscut” should be interpreted according toordinary meaning understood by one of ordinary skill in the art and doesnot imply a specific process to achieve the orientation. The term miscutis not intended to imply any undesirable cut relative to, for example,any of the crystal planes, e.g., c-plane, a-plane. The term miscut isintended to describe a surface orientation slightly tilted with respectto the primary surface crystal plane such as the nonpolar (10-10) GaNplane. Additionally, the term “offcut” or “off-axis” is intended to havea similar meaning as miscut that does not imply any process to achievethe orientation, although there could be other variations,modifications, and alternatives. In yet other embodiments, thecrystalline surface plane is not miscut and/or offcut and/or off-axisbut can be configured using a mechanical and/or chemical and/or physicalprocess to expose any one of the crystalline surfaces describedexplicitly and/or implicitly herein. In specific embodiments, the termsmiscut and/or offcut and/or off-axis are characterized by at least oneor more directions and corresponding magnitudes, although there can beother variations, modifications, and alternatives.

Benefits are achieved over pre-existing techniques using the presentinvention. In particular, the present invention enables a cost-effectivetechnique for growth of large area crystals of non-polar materials,including GaN, AN, InN, InGaN, and AlInGaN and others and other galliumand nitrogen containing materials. In a specific embodiment, the presentmethod and resulting structure are relatively simple and cost effectiveto manufacture for commercial applications. A specific embodiment alsotakes advantage of a combination of techniques, which solve a longstanding need. In a preferred embodiment, the (10-10) non-polarsubstrate and overlying epitaxial crystalline gallium nitride containingfilm are smooth and substantially free from hillocks and the like, whichimprove device performance. As used herein, the term “smooth” generallymeans substantially free from hillocks or other surface imperfections,which lead to degradation in device performance, including reliability,intensity, efficiency, and other parameters that generally defineperformance. Of course, the term smooth would also include otherinterpretations known by one of ordinary skill in the art, as well asvariations, modifications, and alternatives. Depending upon theembodiment, one or more of these benefits may be achieved. These andother benefits may be described throughout the present specification andmore particularly below.

The present invention achieves these benefits and others in the contextof known process technology. However, a further understanding of thenature and advantages of the present invention may be realized byreference to the latter portions of the specification and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is an optical micrograph image representative of aconventional surface region including hillock structures on a non-polarGaN substrate.

FIG. 1( b) is a schematic illustration of a top down view of a hillockstructure.

FIG. 1( c) is a schematic illustration of a cross-sectional view of ahillock structure.

FIG. 2 is a simplified flow diagram of a method for fabricating animproved GaN film according to an embodiment of the present invention.

FIG. 3 is a simplified diagram illustrating various miscuts/offcuts in+/−c/a planes according to one or more embodiments of the presentinvention;

FIGS. 4 through 6 are photographs illustrating the improved GaN filmaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques related generally tooptical devices are provided. More particularly, the present inventionprovides a method and device for fabricating crystalline films foremitting electromagnetic radiation using non-polar (10-10) galliumcontaining substrates such as GaN, MN, InN, InGaN, AlGaN, and AlInGaN,and others. Merely by way of example, the invention can be applied tooptical devices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors, among otherdevices.

In one or more embodiments, the present invention is directed togenerate high efficiency GaN-based light emitting devices operating atwavelengths beyond 400 nm for blue, green, yellow and red emissionaccording to embodiments of the present invention. The proposed devicewill be used as an optical source for various commercial, industrial, orscientific applications. These structures are expected to find utilityin existing applications where blue-violet, blue, green, yellow and redlaser/LED emission is required. An existing application includes HD-DVDand Sony Blu-Ray™ players. One particularly promising application forthese devices is full color displays requiring red-green-blue orblue-yellow color mixing. Another potential application is for opticalcommunication through polymer based fibers where increased wavelengthswill result in reduced loss.

In a specific embodiment, the present invention provides a GaN-basedsemiconductor laser/LED growth/fabrication method to achieve increasedwavelength operation into the blue, green, yellow and red regime onnonpolar GaN substrates where superior laser/LED performance can beexpected according to a specific embodiment. The device relies on smoothsurface region films of epitaxial crystalline GaN containing materialsfor improved device performance. The smooth surface region and thereforehigher quality crystalline material can be derived from epitaxial growthtechniques according to one or more embodiments.

Epitaxial growth on the nonpolar (10-10) plane of bulk GaN has beenemerging and possesses various limitations. Understanding growthparameter space for optimal epitaxial layer deposition is oftenimportant for the realization of high performance electronic onoptoelectronic devices fabricated from the epitaxial layers. At leastone key aspect of the film quality is the morphology. Morphologymanifests itself in large scale features that are on the order of 10s to100s of microns all the way down to the atomic scale on the order ofAngstroms. Achieving smooth epitaxial layers on both the large scale andsmall scale often translate into high performance devices.

FIG. 1( a) is an optical micrograph image which represents aconventional surface region of a non-polar (10-10) oriented galliumnitride epitaxial layer, including hillock structures. The surface shownis representative of epitaxial deposition at atmospheric pressureconditions (e.g. 700-800 Torr) on a non-polar (10-10) GaN substrate. Asshown, non-polar GaN can exhibit very distinct large-scale featuresreferred to herein as hillocks. FIG. 1( b) and FIG. 1( c) are schematicillustrations of a top-down and cross-sectional view of such a hillockfeature. As shown, these hillocks are pyramidal in shape and typicallyelongated in the in the positive and negative a-directions and candemonstrate significantly steep sidewalls in the positive and negativec-directions. Schematic illustration of a top-down view of a pyramidalhillock structure is provided in FIG. 1( b). As shown, shaded regionsrepresent faces of such a hillock structure which are inclined towardthe c+ and c− directions and white regions labeled “a” represent facesof such a hillock structure which are symmetrically inclined toward thea+/a− direction. Such hillocks are typically elongated in the +/−adirection such that the lateral dimension x is larger than thecorresponding perpendicular width dimension y as shown. Lateraldimensions of such hillocks can range from 50-100 microns or greater.The hillocks can have a height scale on the orders of hundreds ofnanometers, therefore they can be disruptive/detrimental tooptoelectronic devices such as laser diodes since the cladding layerswill have varying thickness along the cavity and the gain layers betweenthe cladding layers can have sharp interfaces. As shown, the large-scalemorphological features are predominantly “pyramidal hillocks” or likestructures. These characteristics can lead to increased loss in opticaldevices such as lasers, reduced gain, and perhaps reduced yield andreliability. Of course, there can also be other limitations.

A method according to one or more embodiments for forming a smoothepitaxial film using an offcut or miscut or off-axis substrate isbriefly outlined below.

-   -   1. Provide GaN substrate or boule;    -   2. Perform off-axis miscut of GaN substrate on nonpolar        crystalline planes to expose desired surface region or process        substrate or boule (e.g., mechanical process) to expose off-axis        oriented surface region from the nonpolar (10-10) plane;    -   3. Transfer GaN substrate into MOCVD process chamber;    -   4. Provide a carrier gas selected from nitrogen gas, hydrogen        gas, or a mixture of them;    -   5. Provide a nitrogen bearing species such as ammonia or the        like;    -   4. Raise MOCVD process chamber to growth temperature, e.g., 700        to 1200 Degrees Celsius;    -   5. Maintain the growth temperature within a predetermined range;    -   6. Combine the carrier gas and nitrogen bearing species such as        ammonia with group III precursors such as the indium precursor        species tri-methyl-indium and/or tri-ethyl-indium, the gallium        precursor species tri-methyl-gallium and/or tri-ethyl-gallium,        and/or the aluminum precursor tri-methyl-aluminum into the        chamber;    -   7. Form an epitaxial film containing one or more of the        following layers GaN, InGaN, AlGaN, InAlGaN;    -   8. Cause formation of a surface region of the epitaxial gallium        nitride film substantially free from hillocks and other surface        roughness structures and/or features;    -   9. Repeat steps (7) and (8) for other epitaxial films to form        one or more device structures; and    -   10. Perform other steps, desired.

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting crystalline epitaxial materialwith a surface region that is substantially smooth and free fromhillocks and the like for improved device performance. Although theabove has been described in terms of an off-axis surface configuration,there can be other embodiments having an on-axis configuration using oneor more selected process recipes, which have been described in moredetail throughout the present specification and more particularly below.Other alternatives can also be provided where steps are added, one ormore steps are removed, or one or more steps are provided in a differentsequence without departing from the scope of the claims herein.

As merely an example, the present method can use the following sequenceof steps in forming one or more of the epitaxial growth regions using anMOCVD tool operable at atmospheric pressure or low pressure in someembodiments.

-   -   1. Start;    -   2. Provide a crystalline substrate member comprising a backside        region and a surface region, which has been offcut or miscut or        off-axis;    -   3. Load substrate member into an MOCVD chamber;    -   4. Place substrate member on susceptor, which is provided in the        chamber, to expose the offcut or miscut or off axis surface        region of the substrate member;    -   5. Subject the surface region to a first flow (e.g., derived        from one or more precursor gases including at least an ammonia        containing species, a Group III species, and a first carrier        gas) in a first direction substantially parallel to the surface        region;    -   6. Form a first boundary layer within a vicinity of the surface        region;    -   7. Provide a second flow (e.g., derived from at least a second        carrier gas) in a second direction configured to cause change in        the first boundary layer to a second boundary layer;    -   8. Increase a growth rate of crystalline material formed        overlying the surface region of the crystalline substrate        member;    -   9. Continue crystalline material growth to be substantially free        from hillocks and/or other imperfections;    -   10. Cease flow of precursor gases to stop crystalline growth;    -   11. Perform other steps and repetition of the above, as desired;    -   12. Stop.

The above sequence of steps provides methods according to an embodimentof the present invention. As shown, the method uses a combination ofsteps including a way of forming a film of crystalline material usingMOCVD. In preferred embodiments, the present invention includes amultiflow technique provided at atmospheric pressure (e.g. 700-800 Torr)for formation of high quality gallium nitride containing crystallinefilms that are substantially free from hillocks and other imperfectionsthat lead to crystal degradation. Many other methods, devices, andsystems are also included. Of course, other alternatives can also beprovided where steps are added, one or more steps are removed, or one ormore steps are provided in a different sequence without departing fromthe scope of the claims herein. Additionally, the various methods can beimplemented using a computer code or codes in software, firmware,hardware, or any combination of these. In other embodiments, the presentMOCVD tool can be modified, updated, varied, or combined with otherhardware, processing, and software. Depending upon the embodiment, therecan be other variations, modifications, and alternatives. Furtherdetails of the present method can be found throughout the presentspecification and more particularly below in reference to the Figures.

FIG. 2 is a simplified flow diagram of a method for fabricating animproved GaN film according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims herein. One of ordinary skill in the art wouldrecognize other variations, modifications, and alternatives. In aspecific embodiment, the present method uses a technique using MOCVD asdescribed in, for example, U.S. Provisional Application No. 61/103,238filed Oct. 6, 2008, titled “METHOD AND SYSTEM FOR THIN FILM PROCESSINGUSING SHOWER HEAD DEVICE”, which is hereby incorporated by referenceherein.

As shown, the present method begins with start, step 201. In a specificembodiment, the present method uses a MOCVD reactor configured to carryout the present method. Details of the reactor are provided moreparticularly in U.S. Provisional Application No. 61/103,238 filed Oct.6, 2008, titled “METHOD AND SYSTEM FOR THIN FILM PROCESSING USING SHOWERHEAD DEVICE”, which is hereby incorporated by reference herein.

In a specific embodiment, the present invention provides (step 203) acrystalline substrate member comprising a backside region and a surfaceregion. In a specific embodiment, the crystalline substrate member caninclude, among others, a gallium nitride wafer, or the like. In apreferred embodiment, the substrate is bulk nonpolar (10-10) GaNsubstrate, but can be other materials. More preferably, the substrate isa nonpolar (10-10) GaN substrate, but can be others.

In a specific embodiment, the present method uses a miscut or offcutcrystalline substrate member or boule of GaN, but can be other materialsand does not imply use of a process of achieving the miscut or offcut.As used herein, the term “miscut” should be interpreted according toordinary meaning as understood by one of ordinary skill in the art. Theterm miscut is not intended to imply any undesirable cut relative to,for example, any of the crystal planes, e.g., c-plane, a-plane. The termmiscut is intended to describe a surface orientation slightly tiltedwith respect to the primary surface crystal plane such as the nonpolar(10-10) GaN plane. Additionally, the term “offcut” is intended to have asimilar meaning as miscut, although there could be other variations,modifications, and alternatives. In yet other embodiments, thecrystalline surface plane is not miscut and/or offcut but can beconfigured using a mechanical and/or chemical and/or physical process toexpose any one of the crystalline surfaces described explicitly and/orimplicitly herein. In specific embodiments, the term miscut and/oroffcut and/or off axis is characterized by at least one or moredirections and corresponding magnitudes, although there can be othervariations, modifications, and alternatives.

As shown, the method includes placing or loading (step 205) thesubstrate member into an MOCVD chamber. In a specific embodiment, themethod supplies one or more carrier gases, step 207, and one or morenitrogen bearing precursor gases, step 209, which are described in moredetail below. In one or more embodiments, the crystalline substratemember is provided on a susceptor from the backside to expose thesurface region of the substrate member. The susceptor is preferablyheated using resistive elements or other suitable techniques. In aspecific embodiment, the susceptor is heated (step 211) to a growthtemperature ranging from about 700 to about 1200 Degrees Celsius, butcan be others. Of course, there can be other variations, modifications,and alternatives.

In a specific embodiment, the present method includes subjecting thesurface region of the crystalline substrate to a first flow in a firstdirection substantially parallel to the surface region. In a specificembodiment, the method forms a first boundary layer within a vicinity ofthe surface region. In a specific embodiment, the first boundary layeris believed to have a thickness ranging from about 1 millimeters toabout 1 centimeters, but can be others. Further details of the presentmethod can be found below.

Depending upon the embodiment, the first flow is preferably derived fromone or more precursor gases including at least an ammonia containingspecies, a Group III species (step 213), and a first carrier gas, andpossibly other entities. Ammonia is a Group V precursor according to aspecific embodiment. Other Group V precursors include N₂. In a specificembodiment, the first carrier gas can include hydrogen gas, nitrogengas, argon gas, or other inert species, including combinations. In aspecific embodiment, the Group III precursors include TMGa, TEGa, TMIn,TMAl, dopants (e.g., Cp2Mg, disilane, silane, diethelyl zinc, iron,manganese, or cobalt containing precursors), and other species. Asmerely an example, a preferred combination of miscut/offcut/substratesurface configurations, precursors, and carrier gases are providedbelow.

-   -   Non-polar (10-10) GaN substrate surface configured −0.6 degrees        and greater or preferably −0.8 degrees and greater (and less        than −1.2 degrees) in magnitude toward c-plane (0001);    -   Carrier Gas: Any mixture of N₂ and H₂, but preferably all H₂;    -   Group V Precursor: NH₃; Group III Precursor: TMGa and/or TEGa        and/or TMIn and/or TEIn and/or TMAl; and    -   Optional Dopant Precursor: Disilane, silane, Cp₂Mg;    -   Or    -   Non-polar GaN substrate with no offcut or miscut;    -   Carrier Gas: all N₂; Group V Precursor: NH₃; Group III        Precursor: TMGa and/or TEGa and/or TMIn and/or TEIn and/or TMAl;        and    -   Optional Dopant Precursor: Disilane, silane, Cp₂Mg.

Of course, there can be other variations, modifications, andalternatives.

In a specific embodiment, the present method also includes a step ofproviding a second flow (e.g., derived from at least a second carriergas) in a second direction configured to cause change in the firstboundary layer to a second boundary layer. In a specific embodiment, thesecond direction is normal to the first direction, but can be slightlyvaried according to other embodiments. Additionally, the second boundarylayer facilitates improved crystalline growth as compared to formationusing the first boundary layer embodiment. In a specific embodiment, thesecond flow increases a growth rate of crystalline material formedoverlying the surface region of the crystalline substrate member. Ofcourse, there can be other variations, modifications, and alternatives.

Depending upon the embodiment, the method also continues (step 215) withepitaxial crystalline material growth, which is substantially smooth andfree of hillocks or other imperfections. In a specific embodiment, themethod also can cease flow of precursor gases to stop growth and/orperform other steps. In a specific embodiment, the method stops at step217. In a preferred embodiment, the present method causes formation of agallium nitride containing crystalline material that has a surfaceregion that is substantially free of hillocks and other defects, whichlead to poorer crystal quality and can be detrimental to deviceperformance. In a specific embodiment, at least 90% of the surface areaof the crystalline material is free from pyramidal hillock structures.Of course, there can be other variations, modifications, andalternatives.

The above sequence of steps provides methods according to an embodimentof the present invention. As shown, the method uses a combination ofsteps including a way of forming a film of crystalline material usingMOCVD. In preferred embodiments, the present invention includes amulti-flow technique provided at atmospheric pressure for formation ofhigh quality gallium nitride containing crystalline films, which havesurface regions substantially smooth and free from hillocks and otherdefects or imperfections. Many other methods, devices, system are alsoincluded. Of course, other alternatives can also be provided where stepsare added, one or more steps are removed, or one or more steps areprovided in a different sequence without departing from the scope of theclaims herein. Additionally, the various methods can be implementedusing a computer code or codes in software, firmware, hardware, or anycombination of these. In other embodiments, the present MOCVD tool canbe modified, updated, varied, or combined with other hardware,processing, and software. Depending upon the embodiment, there can beother variations, modifications, and alternatives.

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting crystalline material that issubstantially free from hillocks and the like for improved deviceperformance. Other alternatives can also be provided where steps areadded, one or more steps are removed, or one or more steps are providedin a different sequence without departing from the scope of the claimsherein.

FIG. 3 is a simplified diagram illustrating a wurtzite unit cellstructure characterized by a hexagonal shape including variousmiscuts/offcuts in +/−c/a planes according to one or more embodiments ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the claims herein. One of ordinary skill in the artwould recognize other variations, modifications, and alternatives. Asshown, the wurtzite unit cell comprises gallium nitride material, andillustrates relative orientations of the non-polar m-plane and non-polara-plane. Additionally, the c-plane is also illustrated for referencepurposes. In a specific embodiment, the curved arrows illustrate tiltdirections for miscut or offcut orientations toward the c-plane and/ora-plane. Of course, there can be other variations, modifications, andalternatives.

EXAMPLE

To prove the operation and method of the present invention, we performedvarious experiments. These experiments are merely examples, which shouldnot unduly limit the scope of the claims herein. One of ordinary skillin the art would recognize other variations, modifications, andalternatives. As an example, FIG. 4 presents optical micrograph imagesof the resulting surface morphology in epitaxial films grown with theuse of H₂ carrier gas on (a) an on-axis nonpolar (10-10) GaN substrateand (b) on a nonpolar (10-10) GaN substrate with a substantial miscuttowards the a-plane. FIG. 5 presents images of the resulting surfacemorphology in epitaxial films grown with the use of H₂ carrier gas onnonpolar (10-10) GaN substrates with a varying degree of miscut towardsthe c-plane. FIG. 6 presents images of the resulting surface morphologyin epitaxial films grown on a nominally on-axis nonpolar (10-10) GaNsubstrate with the use of N₂ carrier gas. Further details of ourexperiments are shown below. Of course, there can be other variations,modifications, and alternatives.

In our example, we understood that the hillocking can be controlled withchoice of carrier gases (N₂ or H₂) or a mixture thereof and/or with thechoice of slightly off-axis (e.g., miscut or offcut or formation (e.g.,grinding, polishing etching, or other shaping processes)) nonpolar(10-10) crystal planes. In particular, the hillocking begins todisappear when the substrate is miscut slightly towards the positive ornegative a-plane. See, for example, FIG. 4.

For miscuts greater in magnitude than +/−0.3 degrees toward the a-plane,the epitaxial layers became smooth using a carrier gas of H₂, which hasbeen known. Unexpectedly, we have discovered a marked double peak in the400-440 nm in the emission spectra (as measured by photoluminescence andelectroluminescence) when the a-plane miscut reaches the required amountto achieve smooth morphology. This could be a useful phenomenon is otherdevices, but is not desirable for laser fabrication in such wavelengthrange. It is possible that larger miscuts would eliminate the doublepeaked spectra and would offer some other benefit. Actually, the doublepeak is not observed when the composition of the light emitting layer(s)is adjusted for emission in the 480 nm range. These and otherlimitations have been overcome using the methods and resultingstructures claimed and described herein.

In an effort to achieve smooth epitaxial layers with no double peak withan emission spectra around 405 nm, positive and negative miscuts towardthe c-plane (0001) were explored using growth techniques with H₂ as thecarrier gas. See, for example, FIG. 5. It was found that when positivemiscut angles (for example)+0.3°, towards the plane c-plane (0001) wereused, hillocking was not suppressed and may actually have become moresevere. However, when using negative miscut angles towards the c-plane(0001), the hillocking began to disappear when the miscut angle wasgreater in magnitude than about negative 0.3-0.5 degrees, and would besubstantially free from hillocks when the angle was greater in magnitudethan about negative 0.6 degrees (or increasing miscut in the negative cdirection). There was no double peak observed in the photoluminescenceor electroluminescence spectra demonstrating a promising approach toachieving smooth epitaxial layers along with high quality light emittinglayers for use in optical devices such as laser diodes and lightemitting diodes.

In addition to substrate miscut, choice of MOCVD carrier gas was alsoexplored. It was found that when all H₂ is replaced by N₂ in the carriergas, smooth relatively defect free epitaxy could be achieved on nonpolarsubstrates with nominally non-miscut (0.0+/−0.1 deg) towards the a-planeand c-plane. See, for example, FIG. 6. It is relatively uncommon to useall N₂ as the carrier gas when growing p-type GaN due to reduced dopantincorporation in the lattice, which increases resistance of the materialand degrades device properties. To date, we have fabricated laserdevices demonstrating high performance using all N₂ as the carrier gasin the n-cladding, active region, p-cladding, and even p-contact layer.The device did not demonstrate forward voltages higher than those grownusing all H₂ as the carrier gases. Additionally, we believe that byusing the appropriate mixture of H₂ and N₂ in the carrier gas along withthe appropriate negative miscut towards the c-plane, smooth epitaxiallayers can be achieved that will exhibit p-type GaN electricalproperties equal to those grown in all H₂. As shown in 6(a), an opticalmicrograph image which represents the surface region of a GaN film grownusing N₂ carrier gas on a nonpolar GaN substrate is provided. Thenonpolar GaN substrate has a nominally on-axis (+0.06 towards c-planeand, −0.08 towards a-plane). As shown in 6(a), there are no pyramidalhillocks or other substantial surface morphology features observed. AnAtomic Force Microscopy (AFM) height-scale image of a 50×50 micron areaof the surface region of the GaN film shown in 6(a) is provided in 6(b)and the surface is substantially smooth. An Atomic Force Microscopy(AFM) height-scale image of a 5×5 micron area of the surface region ofthe GaN film shown in 6(a) is provided in 6(c). The surface issubstantially smooth. Of course, there can be other variations,modifications, and alternatives.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

1. An optical device comprising: a gallium- and nitrogen-containingsubstrate having a slightly off-axis non-polar oriented crystallinesurface plane, the slightly off-axis non-polar oriented crystallinesurface plane being inclined from the non-polar (10-10) plane with anegative angle toward the c-plane (0001), a magnitude of the negativeangle being greater than about 0.6 degrees; a gallium- andnitrogen-containing epitaxial layer overlying the slightly off-axisnon-polar oriented crystalline surface plane; and a surface regionoverlying the gallium- and nitrogen-containing epitaxial layer, thesurface region being substantially free from hillocks.
 2. The device ofclaim 1 wherein the magnitude of the negative angle is greater thanabout 0.7 degrees.
 3. The device of claim 1 wherein the magnitude of thenegative angle is greater than about 0.8 degrees.
 4. The device of claim1 wherein the magnitude of the negative angle is greater than about 0.9degrees.
 5. The device of claim 1 wherein the magnitude of the negativeangle is greater than about 1.0 degrees.
 6. The device of claim 1wherein the magnitude of the negative angle is greater than about 1.1degrees.
 7. The device of claim 1 wherein the magnitude of the negativeangle is greater than about 1.2 degrees.
 8. The device of claim 1further comprising an optical device overlying the gallium nitridecontaining epitaxial layer.
 9. The device of claim 1 wherein thegallium- and nitrogen-containing epitaxial layer comprises the surfaceregion that is substantially free from hillocks.
 10. The device of claim1 wherein the gallium- and nitrogen-containing epitaxial layer comprisesthe surface region, and at least 90% of the surface region is free fromhillocks.
 11. The device of claim 1 wherein the gallium- andnitrogen-containing epitaxial layer comprises the surface region, thesurface region being that is substantially free from hillocks withlengths ranging from about 10 microns to about microns.
 12. The deviceof claim 1 wherein the gallium- and nitrogen-containing epitaxial layercomprises the surface region, the surface region being substantiallyfree from hillocks with lengths ranging from 100 microns to about 200microns.
 13. The device of claim 1 wherein the surface region issubstantially free from hillocks with a substantially rectangularfootprint that is elongated in an a-plane direction.
 14. The device ofclaim 1 wherein the surface region is substantially free from hillockswith a pyramidal-like shape.
 15. An optical device comprising: agallium- and nitrogen-containing substrate having a slightly off-axisnon-polar oriented crystalline surface plane, the slightly off-axisnon-polar oriented crystalline surface plane being inclined from thenon-polar (10-10) plane with an angle ranging from about 0 degrees to apredetermined angle toward either or both the c-plane and the a-plane; agallium- and nitrogen-containing epitaxial layer overlying the slightlyoff-axis non-polar oriented crystalline surface plane, the gallium- andnitrogen-containing epitaxial layer comprising at least a region of aquantum well formed by at least an atmospheric pressure epitaxialformation process, the quantum well being at least 3.5 nanometers thick;and a surface region overlying the gallium- and nitrogen-containingepitaxial layer, the surface region being substantially free fromhillocks.
 16. The device of claim 15 wherein the gallium- andnitrogen-containing epitaxial layer comprises multiple quantum wells ormultiple layers including n-type and p-type regions.
 17. The device ofclaim 15 wherein the atmospheric pressure ranges from about 700 Ton toabout 800 Ton.
 18. The device of claim 15 wherein the surface region issubstantially free from hillocks with a substantially rectangularfootprint that is elongated in an a-plane direction.
 19. The device ofclaim 15 wherein the surface region is substantially free from hillockswith a pyramidal-like shape.
 20. The device of claim 15 wherein theslightly off-axis non-polar oriented crystalline surface plane has anon-axis orientation.
 21. The device of claim 15 wherein the gallium- andnitrogen-containing epitaxial layer comprises the surface region that issubstantially free from hillocks.
 22. The device of claim 15 wherein thegallium- and nitrogen-containing epitaxial layer comprises the surfaceregion that is substantially free from hillocks with lengths rangingfrom about 10 microns to about 100 microns.
 23. The device of claim 15wherein the gallium- and nitrogen-containing epitaxial layer comprisesthe surface region that is substantially free from hillocks with lengthsranging from about 100 microns to about 200 microns in length.
 24. Thedevice of claim 15 wherein the gallium- and nitrogen-containingepitaxial layer comprises the surface region, and at least 90% of thesurface region is free from hillocks.
 25. The device of claim 15 whereinthe atmospheric pressure epitaxial formation process uses nitrogen gasas a carrier gas.